Heave Ho! Bacteria Used to Power Motor

Nov. 8, 2006 — Like donkeys turning the wheel of an old-fashioned mill, bacteria turn tiny rotors inside newly designed microscopic machines.

Japanese researchers created the bacteria-powered motors, which they say could be used to power micro-pumps on semiconductor chips designed to analyze fluids, such as blood and drug compounds. And because the machines are biological hybrids, working cells could divide and multiply to replace worn parts.

"In a far future plan, we would like to make micro-robots driven by biological motors. The micro-robot would move around and do mechanical work in the micrometer world," said Yuichi Hiratsuka, a researcher at the Japan Advanced Institute of Science and Technology in Tokyo.

Under the direction of Taro Q.P. Uyeda of the Research Institute for Cell Engineering in Ibaraki, Japan, Hiratsuka and his team published the results of their study in a recent issue of the Proceedings of the National Academies of Science.

The researchers used the bacterium Mycoplasma mobile, a pear-shaped organism that moves along surfaces by gliding. In nature, the bacteria cause a disease in the gills of freshwater fish, but do not infect humans.

The scientists are not sure how the bacterium is able to glide, but they realized it could be a good "donkey" because it usually moves forward in the direction of its tapered end — instead of back and forth or side to side.

To put the bacteria to work, Hiratsuka and his team built a tiny motor just 20 micrometers in diameter out of inorganic silicon coated in gold and sialic acid, which the bacteria naturally need to glide.

The motor contains a square central basin where the organisms are deposited. The bacteria glide along the basin and eventually reach one of four passageways leading to a circular track.

The sialic acid coaxes the bacteria to follow the passageway to the circular track, which encircles a rotor. The rotor has parts that protrude down into the track, where the bacteria are moving.

The bacteria are harnessed to the rotor protuberances just as donkeys are harnessed to a mill wheel. Only instead of a physical connection, the bacteria have a biochemical one.

Prior to depositing the organisms into the basin, the scientists chemically bound a protein to the bacterium's surface. They bound another protein to the rotor's surfaces.

When these two proteins come into contact with each other, they automatically link together.

So when then protein-laden bacteria approached the protein-coated rotor, the organism became affixed to the machine.

It continued gliding, however, thereby forcing the rotor to turn at a rate of up to 2.6 rpm.

"There are a few prior studies utilizing immobilized swimming bacteria to create fluid flow or use free-swimming bacteria to transport cargo. However, these examples of exploiting bacteria seem to me much less sophisticated than [Hiratsuka's] paper," said Henry Hess, assistant professor at the University of Florida in Gainesville, and an expert in biomolecular motors.

Hiratsuka and his team are now working on improving the stability and lifetime of the motor. Although this demonstration used living bacteria to drive the rotor, other biological particles could also be put to work, such as proteins that drive muscle contractions.